Skin evaluation method and skin evaluation device
A profile of optical reflectance relative to a depth within a depth range from an epidermis to an upper layer of a dermis is created based on a coherence signal obtained by optical coherence tomography, an evaluation index is determined by calculating a difference between reflectance at a local minimum point and reflectance at a second local maximum point from the created profile, and skin conditions are evaluated based on the evaluation index.
1. A skin evaluation device for evaluating skin conditions of dullness and translucency, comprising:
a light source configured to emit emission light;
a probe configured to irradiate skin with measurement light and receive reflected light sequentially reflected from inside of the skin which has been irradiated with the measurement light;
an optical path length adjusting unit configured to adjust an optical path length of reference light such that the optical path length is substantially identical to an optical path length of the reflected light received by the probe;
a dividing and multiplexing unit optically connected to the light source, the probe and the optical path length adjusting unit, the dividing and multiplexing unit configured to divide the emission light emitted from the light source into measurement light and reference light to supply the measurement light and the reference light to the probe and the optical path length adjusting unit, respectively, and generate coherent light by multiplexing the reflected light received by the probe and the reference light whose optical path length has been adjusted by the optical path length adjusting unit;
a coherent light detecting unit configured to detect the coherent light generated by the dividing and multiplexing unit;
a signal processing unit configured to create a profile of optical reflectance relative to a depth within a depth range from an epidermis to an upper layer of a dermis based on a coherence signal obtained as a result of detection of the coherent light by the coherent light detecting unit; and
a skin condition evaluating unit configured to evaluate conditions of the skin based on an evaluation index determined according to the profile created by the signal processing unit,
wherein the profile has, as the depth of the skin increases, a first local maximum point that appears at a first position corresponding to a point in an uppermost layer of the epidermis, a local minimum point that appears at a second position after the first local maximum point and a second local maximum point that appears at a third position after the local minimum point,
wherein the evaluation index is a difference or a ratio between any two out of reflectance at the first local maximum point, reflectance at the local minimum point and reflectance at the second local maximum point, and
wherein the skin condition evaluating unit is configured to subject the profile from the signal processing unit to a smoothing process, to recognize the first local maximum point, the local minimum point and the second local maximum point from the profile having undergone the smoothing process, and to calculate the difference or the ratio in reflectance based on values corresponding to the first position, the second position, and the third position in the profile before the smoothing process.
2. The skin evaluation device according to claim 1 , further comprising:
a memory configured to store evaluation results of the skin conditions obtained by the skin condition evaluating unit; and
a display unit configured to display the evaluation results of the skin conditions stored in the memory.